1. Field of the Invention
The present invention relates to noise filters and, in particular, to a noise filter that includes a capacitor.
2. Description of the Related Art
In various types of controlling devices and electronic devices, in order to reduce noise coming through power lines, the incoming noise is filtered out by use of, for example, a noise filter inserted between the power lines.
Such noise filters are described in Patent Documents 1 to 4 (Patent Document 1: Japanese Examined Utility Model Registration Application Publication No. 1-22258; Patent Document 2: Japanese Unexamined Utility Model Registration Application Publication No. 59-22514; Patent Document 3: Japanese Examined Utility Model Registration Application Publication No. 2-18587; Patent Document 4: Japanese Examined Utility Model Registration Application Publication No. 6-31777). For example, a noise filter described in Patent Document 1 includes a multilayer capacitor 111, leads 112 and 113, cylindrical ferrite beads 114 and 115, a ground plate 118, and a feedthrough capacitor 119, as illustrated in FIG. 16.
The leads 112 and 113 are substantially U shaped. At the substantially central portion thereof, electrodes 111a and 111b of the multilayer capacitor 111 are soldered. Both first and second feet 112a of the lead 112 are inserted in the cylindrical ferrite beads 114 and 115. The lead 112 functions as a signal-line lead. The first foot 112a of the lead 112 is inserted in the feedthrough capacitor 119, in addition to the cylindrical ferrite bead 114.
The feedthrough capacitor 119, the second foot 112a of the lead 112, and both first and second feet 113a of the lead 113 pass through holes in the ground plate 118. The outer portions of the cylindrical ferrite beads 114 and 115 are fixed above the ground plate 118 by molding with an insulating resin 120.
The second foot 112a of the lead 112 is insulated from the ground plate 118. The first foot 112a of the lead 112 is soldered to an inner electrode 119a of the feedthrough capacitor 119. An outer electrode 119b of the feedthrough capacitor 119 is soldered to the ground plate 118.
Both of the first and second feet 113a of the lead 113, which functions as a ground lead, are soldered to the ground plate 118. The first foot 112a of the lead 112 and the first foot 113a of the lead 113 function as a pair of, for example, input terminals of the signal-line lead and the ground lead, respectively. The second foot 112a of the lead 112 and the second foot 113a of the lead 113 function as a pair of, for example, output terminals of the signal-line lead and the ground lead, respectively.
The noise filter is a footed discrete type in which the noise filter is implemented in a printed circuit board or the like by insertion of the feet 112a of the lead 112 and the feet 113a of the lead 113 in through holes of the printed circuit board. That is, all the noise filters described in Patent Documents 1 to 4 are the footed discrete type. Therefore, these noise filters cannot be used as a surface-mount component, which meets the future demands of the market.